QCD predictions for the azimuthal asymmetry in charm leptoproduction for the COMPASS kinematics

Research paper by A.V. Efremov, N.Ya. Ivanov, O.V. Teryaev

Indexed on: 11 Jul '17Published on: 27 Jun '17Published in: Physics Letters B


We present the QCD predictions for the azimuthal cos⁡2φcos⁡2φ asymmetry in charm leptoproduction for the kinematics of the COMPASS experiment at CERN. The asymmetry is predicted to be large, about 15%. The radiative corrections to the QCD predictions for the cos⁡2φcos⁡2φ distribution are estimated to be small, less than 10%. Our calculations show that the azimuthal asymmetry in charm production is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the input parameters. We analyze the nonperturbative contributions to the cos⁡2φcos⁡2φ distribution due to the gluon transverse motion in the target and the c-quark fragmentation. Because of the c-quark low mass, the nonperturbative contributions are expected to be sizable, about (30–40)%. We conclude that extraction of the azimuthal asymmetries from available COMPASS data will provide valuable information about the transverse momentum dependent distribution of the gluon in the proton and the c  -quark hadronization mechanism. Finally, we discuss the cos⁡2φcos⁡2φ asymmetry as a probe of the gluonic analogue of the Boer–Mulders function, <img height="22" border="0" style="vertical-align:bottom" width="22" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0370269317305336-si3.gif">h1⊥g, describing the linear polarization of gluons inside unpolarized proton.

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